Synchronization of recordings

Abstract

A playback permits two or more recordings associated with time codes to be retrieved synchronously at variable relative speeds. A master playback unit retrieves a master video recording and the associated master time code and a slave playback unit retrieves a slave audio recording and the associated slave time code. A microprocessor scales the slave audio time code to produce virtual slave time code, and the master and virtual slave time codes are compared to produce a virtual offset which is maintained substantially constant with speed control thereby synchronizing the operation of the master and slave playback units. An operator can select the magnitude of the virtual offset, and can also select the scaling factor used to produce the virtual slave code thereby varying the retrieval speed of the slave playback unit relative to the master playback unit, effectively compressing or expanding the slave recording relative to the master recording. The operator can also advance the master tape to a required position and then advance the slave tape in response to the virtual offset to a corresponding position either manually or automatically. Accordingly, both variable speed synchronization and convenient advancing of master and slave tapes to corresponding positions are possible.

I claim: 
     
       1. A method of synchronizing contemporaneous playback of first and second recordings at different relative playback speeds thereby to compress or expand playback of the first recording relative to playback of the second recording and of thereafter advancing the recordings to desired respective portions thereof that corresponded during such contemporaneous playback, the first recording being one of an audio recording and a video recording played back on a first playback unit that produces a first time code identifying sequentially spaced-apart portions of the first recording during playback and advancing of the first recording, the second recording being the other of the audio recording and the video recording played back on a second playback unit that produces a second time code identifying sequentially spaced-apart portions of the second recording during playback and advancing of the second recording, the method comprising: selecting a constant offset reference;   continually transforming the first time code into a virtual time code according to a preselected relationship;   comparing the second time code with the virtual time code and generating a virtual offset representing the difference between the virtual time code and the   second time code;   controlling the speed of playback of the first recording relative to the speed of playback of the second recording during the contemporaneous playback such that the virtual offset is substantially equal to the constant offset reference throughout the contemporaneous playback thereby synchronizing the   contemporaneous playback of the first and second recording at different relative speeds determined by the preselected relationship, the relationship being preselected to produce one of an expansion and a contraction of the playback of the first recording relative to the playback of the second recording during the controlling of the playback speed; and,   advancing the recordings after the contemporaneous playback in response to the virtual and second time codes to a desired portions of the second recording and to a portion of the first recording for which the virtual time code corresponds to the time code of the second recording plus the constant offset reference whereby the recordings are advanced to desired portions thereof that corresponding during the contemporaneous playback.   
     
     
       2. The method of claim 1 comprising continually displaying the virtual time code, the second time code, and the virtual offset, the advancing of the recordings comprising: manually actuating the second playback unit such that the second recording is advanced to the desired portion thereof and the second time code value identifying the desired portion thereof is displayed;   manually actuating the first playback unit such that first recording is advanced until the displayed virtual time corresponds to the second time code plus the constant offset reference.   
     
     
       3. The method of claim 1 comprising continually displaying the virtual time code, the second time code, and the virtual offset, the advancing of the recordings comprising: manually actuating the second playback unit such that the second recording is advanced to the desired portion thereof;   automatically advancing the first playback unit in response to the virtual time code and the second time code until the virtual time corresponds to the second time code plus the constant offset reference.   
     
     
       4. The method of claim 1 in which the preselected relationship is a scaling of the first time code by a constant preselected scaling factor. 
     
     
       5. The method of claim 1 in which the first recording is the audio recording and the second recording is the video recording. 
     
     
       6. Apparatus for synchronizing contemporaneous playback of first and second recordings at different relative playback speeds thereby to compress or expand playback of the first recording relative to playback of the second recording and of thereafter advancing the recordings to desired respective portions thereof that corresponded during such contemporaneous playback, the first recording being one of an audio recording and a video recording played back on a first playback unit that produces a first time code identifying sequentially spaced-apart portions of the first recording during playback and advancing of the first recording, the second recording being the other of the audio recording and the video recording played back on a second playback unit that produces a second time code identifying sequentially spaced-apart portions of the second recording during playback and advancing of the second recording, the apparatus comprising: means permitting an operator to specify a desired relationship for transformation of the first time code into a virtual time code;   means for transforming the first time code into the virtual slave time code according to the specified relationship;   means for comparing the second time code with the virtual time code and generating a virtual offset representing the difference between the virtual time code and the second time code;   means for controlling the speed of playback of the first recording relative to the speed of playback of the second recording during the contemporaneous playback such that the virtual offset corresponds to the constant offset reference thereby synchronizing the contemporaneous playback of the recordings at different relative speeds determined by the specified relationship and producing one of an expansion and a contraction of the playback of the first recording relative to the playback of the second recording; and,   means permitting the operator to advance the recordings after the contemporaneous playback in response to the virtual and second time codes to a desired portion of the second recording and to a portion of the first recording for which the virtual time code corresponds to the time code of the second recording plus the constant offset reference thereby advancing the recordings to desired portions thereof that corresponded during the contemporaneous playback.   
     
     
       7. The apparatus of claim 6 in which the means permitting the operator to advance the recordings after the contemporaneous playback comprise display means for continually displaying the virtual time code, the second time code, and the virtual offset. 
     
     
       8. The apparatus of claim 7 further comprising: means permitting the operator to manually operate the second playback unit such that the second recording is advanced to the desired portion thereof and the second time code value associated with the second recording is displayed;   means permitting the operator to manually operate the second playback unit such that the first recording is advanced until the displayed virtual time corresponds to the displayed second time code value plus the constant offset reference.   
     
     
       9. The apparatus of claim 7 further comprising; means permitting the operator to manually operate the second playback unit such that the second recording is advanced to the desired portion thereof;   means for automatically advancing the first playback unit in response to the virtual time code and the second time code until the virtual time corresponds to the second time code plus the constant offset reference.   
     
     
       10. The apparatus of claim 6 in which: the transforming means scale the first time code by a constant scaling factor; and,   the means permitting the operator to specify the relationship permit the operator to specify the magnitude of the scaling factor.   
     
     
       11. Apparatus for synchronizing contemporaneous playback of first and second recordings at different relative playback speeds thereby to compress or expand playback of the first recording relative to playback of the second recording and of thereafter advancing the recordings to desired respective portions thereof that corresponded during such contemporaneous playback, the first recording being one of an audio recording and a video recording played back on a first playback unit that produces a first time code identifying sequentially spaced-apart portions of the first recording during playback and advancing of the first recording, the second recording being the other of the audio recording and the video recording played back on a second playback unit that produces a second time code identifying sequentially spaced-apart portions of the second recording during playback and advancing of the second recording, the apparatus comprising: means permitting an operator to specify a desired relationship for transformation of the first time code into a virtual time code;   means for transforming the first time code into the virtual slave time code according to the specified relationship;   means for comparing the second time code with the virtual time code and generating a virtual offset representing the difference between the virtual time code and the second time code;   means for controlling the speed of playback of the first recording relative to the speed of playback of the second recording during the contemporaneous playback such that the virtual offset corresponds to the constant offset reference thereby synchronizing the contemporaneous playback of the recordings at different relative speeds determined by the specified relationship and producing one of an expansion and a contraction of the playback of the first recording relative to the playback of the second recording; and,   means for continually displaying the virtual time code, the second time code and the virtual offset whereby the operator can advance the recordings by means of their respective playback units after the contemporaneous playback to a desired portion of the second recording and to a portion of the first recording for which the virtual time code corresponds to the time code of the second recording plus the constant offset reference.